Permit attaching files to new records

Closes #31164.

2 files changed, 9 insertions, 5 deletions

diff --git a/activestorage/lib/active_storage/attached/many.rb b/activestorage/lib/active_storage/attached/many.rb
index 0b3400bccf..6eace65b79 100644
--- a/activestorage/lib/active_storage/attached/many.rb
+++ b/activestorage/lib/active_storage/attached/many.rb
@@ -20,7 +20,11 @@ module ActiveStorage
     #   document.images.attach([ first_blob, second_blob ])
     def attach(*attachables)
       attachables.flatten.collect do |attachable|
-        attachments.create!(name: name, blob: create_blob_from(attachable))
+        if record.new_record?
+          attachments.build(record: record, blob: create_blob_from(attachable))
+        else
+          attachments.create!(record: record, blob: create_blob_from(attachable))
+        end
       end
     end
 
diff --git a/activestorage/lib/active_storage/attached/one.rb b/activestorage/lib/active_storage/attached/one.rb
index 7092f6b109..0244232b2c 100644
--- a/activestorage/lib/active_storage/attached/one.rb
+++ b/activestorage/lib/active_storage/attached/one.rb
@@ -23,7 +23,7 @@ module ActiveStorage
       if attached? && dependent == :purge_later
         replace attachable
       else
-        write_attachment create_attachment_from(attachable)
+        write_attachment build_attachment_from(attachable)
       end
     end
 
@@ -67,13 +67,13 @@ module ActiveStorage
         blob.tap do
           transaction do
             detach
-            write_attachment create_attachment_from(attachable)
+            write_attachment build_attachment_from(attachable)
           end
         end.purge_later
       end
 
-      def create_attachment_from(attachable)
-        ActiveStorage::Attachment.create!(record: record, name: name, blob: create_blob_from(attachable))
+      def build_attachment_from(attachable)
+        ActiveStorage::Attachment.new(record: record, name: name, blob: create_blob_from(attachable))
       end
 
       def write_attachment(attachment)